This invention relates to an improved method for the bulk polymerization of vinyl chloride monomer or a monomeric mixture composed mainly of vinyl chloride.
In the prior art bulk polymerization of vinyl chloride, it is known that polymer scale deposits on the inner walls of a polymerization vessel and the surfaces of agitator blades and other implements in contact with the monomer. It is therefore necessary to clean the polymerization vessel and the implements after each or several of the polymerization runs. The removal of such scale usually requires a great deal of labor and time. Furthermore, the deposition of polymer scale on the inner walls a polymerization vessel reduces the heat transfer of the vessel walls, resulting in lowering of the productivity. Further any released scale entering into the polymer product results in a reduction of polymer quality. Finally, the cleaning or descaling work necessary to remove the scale causes caused a very serious health problem to the workers. This is due to the toxicity of the vinyl chloride monomer absorbed in the polymer scale.
Accordingly, various attempts have been made to prevent the deposition of polymer scale in the bulk polymerization of vinyl chloride by improving design of the agitator blades and other implements. No particular success has been obtained with this approach.